Paper machine pressurized headbox control of stock flow



1966 e. L. HARMAN, JR., ETAL 3,293,120

PAPERMACHINE PRESSURIZED HEADBOX CONTROL OF STOCK FLOW Filed July 29,1964 l3 T comPg E ssEo f4 TO ATMOSPHERE INVENTORS AND JACK F. SHANNON BY*-STOCK FLOW 1, *7 M HEADBOX PRESS. ATTORNEY GEORGE L4 HARMAN JR UnitedStates Patent Oflfice 3,293,12' Patented Dec. 20, 1966 3,293,120 PAPERMACHINE PRESSURIZED HEADBOX CONTROL OF STOCK FLOW George L. Harman, Jr.and Jack F. Shannon, Cleveland,

Ohio, assignors to Bailey Meter Company, a corporation of Delaware FiledJuly 29, 1964, Ser. No. 385,920, 6 Claims. (Cl. 162253) This inventionrelates to a control system for a paper machine and more particularly toa control system for a pressurized headbox supplying stock to a webforming traveling screen.

It has been established that preferably the spouting velocity, that isthe rate of discharge of stock from the headbox, should be properlycorrelated with the velocity of the traveling screen in order to producea satisfactory web. If the spouting velocity deviates substantially fromthat of the screen poor paper formation may result or a web havingundesirable variations in thickness may be formed. As the velocity ofthe screen is adjusted from time to time, in response to observationsand measurements made on the web or finished paper, and further as thevelocity of the screen will vary with changes in voltage, frequency andthe like of the drive motors for the screen it follows thatcorresponding and immediate changes should be made in the headboxspouting velocity.

Heretofore as taught by Eastwood in United States Patent 3,077,924 andby De Mers in United States Patent 1,93 6,049 correlation between screenvelocity and spouting velocity may be obtained by varying the level ofstock in the headbox. The advent of the pressurized headbox, however,that is a headbox wherein a pad of compressed air is maintained abovethe level of stock, while permitting higher spouting velocities andhence higher machine speeds, has presented a new control problem.

Accordingly, it is an object of this invention to provide a control fora paper machine headbox of the pressurized type.

It is a further object to provide a pressurized headbox control whereinthe spouting velocity of the stock immediately and in proper proportionfollows variations in speed of the traveling screen.

It is another object of this invention to provide a pressurized hcadboxcontrol wherein the level of stock in the headbox is maintained at apredetermined desired value, hence assisting in the maintenance of aspouting stock of uniform mixture and quality.

Still another object is to provide a pressurized headbox control whichwhile reacting instantaneously to changes in machine speed is stable inoperation, produces the desired results without cycling, causing neitherfluctuations in the quality of the spouting stock, nor undesiredfluctuations in the rate of stock fed to the headbox.

These and other objects will be apparent from the de scription to followand from the drawings in which:

FIG. 1 is a cycle diagram of a typical pressurized headbox and travelingscreen of a paper making machine to which our control may be applied.

FIG. 2 is a diagrammatic illustration of a control embodying ourinvention arranged for application to the cycle shown in FIG. 1.

FIG. 3 illustrates a modified form of our invention.

Referring now to FIG. 1 we therein show a pressurized headbox 1 havingan adjustable orifice 2, or slice as it is commonly called, for spoutingstock on a traveling screen 3. The screen 3 is provided with the usualbreast roll 4 and a couch roll 5 located at opposite ends of the screen,the latter being driven by any suitable means such as an electric motoror the like (not shown).

Below the screen 3 is a pit 6 for receiving the water drained from thestock (white water) which is recycled through a conduit 7 to the stocksupply system. Feedstock is supplied the headbox 1 by means of a fanpump 8 through a conduit 9. Makeup stock is introduced into the stocksupply system through a conduit 10. We have shown in conduits 7 and 10valves 11 and 12 respectively as representative of any conventionalmeans, manual or automatic, for maintaining a desired ratio betweenrecycled white water and makeup stock.

Compressed air from any suitable source (not shown) is introduced intothe headbox through a conduit 13 to pressurize the headbox and maintainan air pad above the level of stock. The velocity of the stock spoutingfrom the orifice 2 may be varied by varying the differential pressureacross the orfice. This differential pressure is equal to the total headwithin the headbox, that is the head produced by the weight of stockabove the,

orifice plus the pressure of the air pad. Conveniently, therefore, thespouting velocity can be varied by varying the pressure of the air padand to accomplish this we show in conduit 13 valves 14 and 15, the valve14 controlling the supply of compressed air to the headbox and the valve15 controlling the air wasted therefrom to the atmosphere. Any desiredair pressure may be maintained by proper adjustment of valves 14 and 15.

It is evident that as the spouting velocity of stock through the orificetube varies so must the supply of stock to the headbox vary to maintaina desired level of stock within the headbox. We accordingly show asrepresentative of a suitable control means for the stock input a valve16 disposed in the conduit 9. As evident flow control of the feedstockcould also be obtained, if desired, by varying the speed of pump 8solely or in combination with adjustment of valve 16.

As this description is addressed to those skilled in the art we havepurposely, in FIG. 1, shown the headbox and related equipment inskeleton form, omitting features which while necessary and while knownin the art are not essential to an understanding of our invention.

In FIG. 2 is illustrated diagrammatically a control system embodying ourinvention arranged for application to the pressurized headbox shown inFIG. 1. Measuring instruments and final control elements shown in FIG. 2have been referenced into FIG. 1. While in FIG. 2 we have illustrated acontrol system of the so-called pneumatically operated type it isapparent that our invention may equally as well be incorporated inelectric or hydraulic instrumentalities.

Referring now to FIG. 2 there is illustrated a control system for apressurized headbox which maintains the spouting velocity of the stockin desired relation to screen speed and further maintains the level ofstock in the headboX at a predetermined or desired value. Therein weshow a transmitter 17 responsive to the diiferential across the orifice2, or in other words, responsive to the total head within the headbox 1,which establishes a pneumatic loading pressure proportional to thedifferential. This loading pressure is transmitted through relays 21 and18 to valves 14 and 15 arranged to operate in opposite directions. Thusas the pressure established by transmitter 17 increases indicating anincrease in total head, theoutput pressure of relay 18 will decreaseproportionally causing valve 14 to move in a closing direction and valve15 to move in an opening direction to thereby decrease the pressure ofthe air pad.

The relay 18 may be of the type described in Panich United States Patent2,805,678 and is preferably of the socalled proportional plus reset typeincorporating a proportional band adjustment and having automaticadjustable reset. The set point of relay 18, which determines thedifferential pressure maintained by the control, is automaticallymaintained proportional to screen velocity. Thus, as shown, the loadingpressure established by a screen speed transmitter 20 is introduced intorelay 18 through conduit 23. The transmitter 20 is driven, as shown inFIG. 1, by the couch roll 5 through any suitable means such as a belt30.

As the loading pressure established by the transmitter 20 variesdirectly with the velocity of the traveling screen whereas the spoutingvelocity of the stock through the orifice 2 varies as the square root ofthe total head, a relay 21 is interposed between transmitter 17 andrelay 18 to extract the square root of the loading pressure establishedby transmitter 17. Hence changes in machine speed effecting proportioalchanges in the loading pressure established by transmitter 20 willeffect directly proportional changes in the velocity of the stockspouting through the orifice 2. The relay 21 may take anyone of severalwell known forms and if desired can be incorporated in the transmitter17 as taught by I ack F. Shannon in United States Patent 2,986,151.Conversely, a relay vmay be provided to generate a loading pressureproportional to square of the output pressure of speed transmitter 2t)and inserted in conduit 23. In essence with the control so far describedthe transmitter 20 establishes a demand signal calling for a preciseditferential pressure, which difiterental pressure is then maintained bythe constant difierential pressure control.

The speed transmitter 20 also establishes the demand for stock flow tothe headbox so that the rate of stock fed to the headbox 1 is maintainedequal to the output therefrom. As shown there is provided in conduit 9 aflow transmitter 22 generating a loading pressure proportional to thesquare of the rate of flow of stock to the headbox 1. This loadingpressure through relays 28 and 25 operates valve 16 to maintain thestock feed at the set point value established in relay 25 which, asshown, is responsive to the loading pressure generated by the speedtransmitter 20 through an algebraic summing relay 24.

Thus the set point of the constant flow control is adjusted inproportion to changes in screen speed.

To compensate for instrument and control component inaccuracies and tomaintain a predetermined level of stock within the headbox, the loadingpressure generated by speed transmitter 20 is modified in algebraicsumming relay 24 in accordance with changes in level of stock. We show alevel transmitter 26 which establishes a loading pressure proportionalto level, which through a proportional plus reset relay 27 is elfectivein relay 24 for modifying the loading pressure generated by speedtransmitter 20.

The relay 28 similar to the .relay 21 is provided to extract the squareroot of the loading pressure generated by the transmitter 22. Thisrelay, as discussed with ref-' erence to relay 21, may be made integralwith the transmitter 22 so that a loading pressure varying in directproportion to stock flow may be generated.

In the embodiment of our invention shown in FIG.

2 the rate of flow of feedstock to the headbox 1 is maintainedproportional to screen speed and inferentially maintained equal to therate of flow of stock spouting from orifice 2. It is evident, however,if the rate of flow of feedstock to the headbox 1, established by thedemand signal from speed transmitter 20, is not equal to the rate offlow of stock spouting from orifice 2, the level of stock in the headboxwill tend to vary which will operate through the constant level controlto modify the set point of the constant flow control as established bythe demand signal as required to restore the desired level andproportionality between stock flow to and from the headbox.

In FIG. 3 we show a modification wherein the rate of flow of stock fedto the headbox is ratioed directly with the flow through the orifice 2.Therein the set point of the constant flow control of stock feed isadjusted from the loading pressure generated by relay 21 and henceadjusted in accordance with the square :root of the loading pressureestablished by the total head transmitter 17. Otherwise the controlshown in FIG. 3 operates as explained with reference to FIG. 2.

What We claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a control system for a papermaking machine having a traveling webforming screen and a pressurized headbox containing a pool of stock andhaving an orifice for spouting stock on said screen, a first conduit forsupplying stock to the headbox, a second conduit for supplyingcompressed air to the headb-ox above the level of stock to pressurizethe headboX, means producing a signal corresponding to the velocity ofthe traveling screen, a first valve in said first conduit under thecontrol of said signal maintaining the rate of flow of stock to theheadbox proportional to the velocity of the traveling screen, a supplyand waste valve means in said second conduit under the control of saidfirst signal maintaining the total head in said headbox proportional tothe velocity of the traveling screen, means producing a second signalproportional to the level of stock in the headbox and means modifyingthe control of said first valve by said second signal in accordance withchanges in the level of stock in the headbox.

2. In a control system for a papermaking machine having a traveling webforming screen and a pressurized headbox containing a pool of stock andhaving an orifice for spouting stock on said screen, comprising incombination, means producing a first signal corresponding to thevelocity of the screen, means producing a second signal corresponding tothe level of stock in the headbox, means producing a third signalcorresponding to the flow of stock to the headbox, and means under thejoint control of all of said signals regulating the flow of stock tosaid headbox.

3. In a control system for a papermak-ing machine having a traveling webforming screen and a pressurized headbox containing a pool of stock andhaving an orifice for spouting stock on the screen, comprising incombination, first means regulating the pressure in the headbox tomaintain a constant diilerential pressure across the orifice, secondmeans responsive to the velocity of the traveling screen adjusting theconstant difierential pressure maintained by said first means inaccordance with changes in the velocity of the screen, constant flowcontrol means of the stock to the headbox, a third means responsive tothe level of stock in the headbox, and means under the control of saidsecond and third means adjusting the rate of flow of stock maintained bysaid constant flow control means to establish a flow of stockproportional to the velocity of the screen modified by changes in thelevel of stock in the headbox.

4. In a control system for a papermaking machine having a traveling Webforming screen and a headbox containing a pool of stock and an orificefor spouting stock on the screen, comprising in combination, constantflow control means having an adjustable setpoint of the stock suppliedto the headbox, means producing a first control signal corresponding tothe velocity of the traveling screen, means producing a second controlsignal corresponding to the level of stock in the headbox and meansadjusting the setpoint of the constant flow control means responsive tosaid first and second control signals to maintain the rate of flowofstock to the headbox in proportion to the velocity of the travelingscreen modified in accordance with changes in level of stock in theheadbox.

5. In a control system for a papermaking machine having a traveling webforming screen and a pressurized headbox containing a pool of stock andan orifice for spouting stock on the screen, comprising in combination,constant flow control means having an adjustable setpoint of the stocksupplied the headbox, means having an adjustable setpoint for regulatingthe pressure in the headbox to maintain a constant differential acrossthe orifice, means producing a control signal corresponding to thevelocity of the traveling screen, means under the control of said signaladjusting the setpoint of said constant differential pressure controlmeans to maintain the velocity of the stock through said orifice inproportion to the velocity of the traveling screen, means under thecontrol of said signal adjusting the setpoint of said constant flowcontrol means to maintain the flow of stock to the headbox proportionalto the velocity of the traveling screen, means producing a controlsignal corresponding to changes in the level of the pool of stock in theheadbox and means responsive to said last named control signal modifyingthe adjustment of the setpoint of said constant flow control means inaccordance with changes in the level of the pool of stock in saidheadbox.

6. In a control system for a papermaking machine having a traveling Webforming screen and a pressurized headbox containing a pool of stock andan orifice for spouting stock on the screen, comprising in combination,constant flow control means having an adjustable setpoint of the stocksupplied the headbox, means producing a control signal corresponding tothe differential pressure across said orifice, means under the controlof said signal for regulating the pressure in the headbox, means underthe control of said signal adjusting the setpoint of said constant flowcontrol means to maintain the flow of stock to the headbox proportionalto the velocity of the screen, means producing a control signalcorresponding to changes in level of the pool of stock in the headboxand means responsive to said last named control signal modifying theadjustment of the setpoint of said constant flow control means inaccordance With changes in level of stock in said headbox.

References Cited by the Examiner UNITED STATES PATENTS 2,677,991 5/1954Goumeniouk l62259 3,077,924 2/ 1963 Eastwood l62-259 DONALL H.SYLVESTER, Primary Examiner.

S. LEON BASHORE, Examiner.

2. IN A CONTROL SYSTEM FOR A PAPERMAKING MACHINE HAVING A TRAVELLING WEBFORMING SCREEN AND A PRESSURIZED HEADBOX CONTAINING A POOL OF STOCK ANDHAVING AN ORIFICE FOR SPOUTING STOCK ON SAID SCREEN, COMPRISING INCOMBINATION, MEANS PRODUCING A FIRST SIGNAL CORRESPONDING TO THEVELOCITY OF THE SCREEN, MEANS PRODUCING A SECOND SIGNAL CORRESPONDING TOTHE LEVEL OF STOCK IN THE HEADBOX, MEANS PRODUCING A THIRD SIGNALCORRESPONDING TO THE FLOW OF STOCK TO THE HEADBOX, AND MEANS UNDER THEJOINT CONTROL OF ALL OF SAID SIGNALS REGULATING THE FLOW OF STOCK TOSAID HEADBOX.